Tying the knot April 29: And Prince William and Kate Middleton may ascend their thrones sooner than thought if Queen Elizabeth II steps aside early.

MORE WILL & KATE BOOKS ON THE WAY

William & Kate: A Royal Love Story, in stores (HarperCollins /Sterling, $19.95), by James Clench, the royals reporter for The Sun, the U.K.'s biggest-selling newspaper.

William & Kate: Celebrating a Royal Engagement, due Feb. 1 (Trafalgar Square $24.95), features more than 130 photographs by leading royals photographer Robin Nunn with text by royals writer Jonathan Hayden.

William and Kate: A Royal Wedding, to be published by Michael O'Mara Books around the time of the wedding, is forthcoming from Andrew Morton, the British journalist who first revealed the unhappy details of the disintegration of Diana's marriage in his 1992 book Diana: Her True Story.

By Maria Puente, USA TODAY

Queen Kate, sooner than later?

That's the most startling revelation in William and Kate: A Royal Love Story, Christopher Andersen's new book about Prince William and his fiancée, Catherine "Kate" Middleton.

The book, about what Andersen calls "the first epic love story of the 21st century," is being published Tuesday (Gallery, $26). It's one of at least four new Will and Kate books already out or forthcoming since the Nov. 16 engagement announcement that the couple will marry April 29 at Westminster Abbey in London. Like bookies and souvenir makers, publishers are rushing to take advantage of worldwide interest in the royal wedding.

Andersen, a longtime royals watcher who finished his book nearly two months before the engagement, reports that his unnamed palace sources say William's grandmother has agreed to at least consider stepping aside early (perhaps after her Diamond Jubilee in 2012) so that William's father, Prince Charles, could become king at a reasonably young age. Charles just turned 62; she turns 85 next year, and her mother lived to nearly 102.

"They don't want Charles to succeed at age 77, which would be the oldest since William IV" in 1830, Andersen says. It would mean William's turn on the throne could come sooner and Middleton would become "the first true commoner queen, the first non-aristocrat, in 350 years," Andersen says.

If it happens, it would be big news, especially for the British, long accustomed to believing the queen would never retire or abdicate before her death.

Even though she has been William's girlfriend for nearly a decade, Middleton is still not well known thanks to fierce protection from the media-loathing William. Andersen says his research found that, despite a few embarrassing family relations (such as her occasionally cross-dressing younger brother, James), he could find no dirt on the couple.

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